1. Field of the Invention
The present invention relates to a lens-fitted photo film unit previously loaded with a photo film, more particularly to a lens-fitted photo film unit changeable in position of a taking lens depending upon a flash photography mode or a daylight photography mode.
2. Description of the Prior Art
As is well known, there is a lens-fitted photo film unit that facilitates taking photographs for any user. At a manufacturing plant, the lens-fitted photo film unit is previously loaded with a photo film being unexposed, and has a simple exposure mechanism. And some types of the lens-fitted photo film unit for retail sale respectively built-in a flash device so that it is possible to take photographs even at night or in rear light. The lens-fitted photo film unit having the flash device is provided with a flash selection switch that makes external operation possible. If the flash selection switch is slid from an OFF position to an ON position, a flash photography mode is selected so that the flash device emits flash light synchronized with a shutter.
The lens-fitted photo film unit has a fixed focus taking lens, which has one or two lens elements. In a daylight photography mode where the flash device is unused, it is possible to take the photographs at various subject distances from a short distance like a portrait to a long distance like a landscape photograph. To cover the wide field of the subject distances, the taking lens having a short focal length and a large f-number (aperture value) is used to perform pan-focus.
A range of distance at which a subject can be lit up by the flash device depends on a guide number, which is generally determined within the range of approximately 3 to 4 meters. In the flash photography, a main subject is usually a person, so that it is necessary to take sharper photographs. However, as the pan-focus is performed with the taking lens, it is inevitable that sharpness of an image being obtained by the flash photography becomes insufficient to some extent.
In view of the foregoing, an object of the present invention is to provide a lens-fitted photo film unit for taking sharp photographs especially in a flash photography.
Another object of the present invention is to provide a lens-fitted photo film unit for obtaining suitable sharpness in wide field in a daylight photography.
A further object of the present invention is to provide a lens-fitted photo film unit changeable in size of a stop aperture depending upon a flash photography mode or a daylight photography mode.
The above and other objects can be accomplished by shifting a taking lens in response to operation of a flash selection member, and setting an objective focal point in the flash photography mode to a short distance compared with an objective focal point in the daylight photography mode. In the flash photography mode, the lens-fitted photo film unit is focused on a short-distance zone, so that sharpness of such an image of a person lit up by flash light becomes high. In contrast with that, in the daylight photography mode where a flash device is unused, pan-focus keeps the sharpness of the image suitably in the wide range from the short distance to a long distance.
In the embodiments of the present invention, a stop changing device is disposed for selecting a small stop aperture in the daylight photography mode or a large stop aperture in the flash photography mode in response to the operations of the flash selection member. In the flash photography mode of another preferred embodiment of the present invention, the small stop aperture is selected if subject brightness is above a predetermined level, and the large stop aperture is selected if he subject brightness is below the predetermined level.
According to the present invention, in the flash photography mode, the taking lens is shifted to a suitable position for focusing on the short-distance zone, so that the sharpness of the image of a person to be important can be high. The taking lens needs no extra operation and has a simple structure as is shifted in response to the flash selection member. Further in the flash photography mode, as the stop aperture can be changed for one having a suitable size corresponding to the subject brightness, exposure amount on a person in rear light is appropriate, and the exposure amount on a person within the short-distance zone appropriate in the flash photography at night.